Conventional deep-sea telecommunication cables are designed to interconnect ground user networks within high-speed paying intercontinental links. These electro-optical cables are highly reliable and have a lifetime of many decades. They are deployed conventionally from the surface by cable ships. They must be particularly reinforced as they must be resistant to deployment efforts due to their linear weight and surface accelerations. Links of a few hundred kilometers are produced in one piece in a factory by assembling cable segments by using repeaters (about every fifty kilometers) as well as bypasses for communicating with other ground user networks (an island for example).
This technology perfectly meets the needs of ground users but is not necessarily adapted to users requiring to be connected on the sea floor. However, the deep-sea sensor networks which are currently under study are either adopting or planning to adopt this technology, mainly for availability and reliability purposes.
According to this technology, in a first phase, the network is deployed continuously from the shore by a cable ship, from point-of-use to point-of-use. The network is formed by transport segments connected in a factory by repeaters or bypasses in order to serve the various points-of-use. In a second phase, nodes (or junction boxes) are set-up and connected at the ends of these bypasses on the sea floor by an underwater vehicle. In a third phase, these sensors are set-up and connected on the sea-floor by an underwater vehicle.
The advantage of this concept is to use for the network, cables and deployment methods that are proven in the telecommunications field. Another advantage is that these electro-optical cables designed to supply repeaters in line can also electrically supply the sensors. Such cables can transmit at high voltage, power levels of around hundreds of kilowatts.
The disadvantage is that these cables are heavy (a ton per kilometer) and are costly. Moreover, their deployment requires specialized and costly cable ships.
However, despite the existence of other communication concepts, there is no way to avoid the (optical) cable for sea floor communications over a great distance. The acoustic transmission concept is not adapted for great distances and requires the use of relay stations every ten kilometers. Moreover, the bandwidth is very limited and the energy per transmitted bit is high. The Hertzian transmission concept by means of surface buoys requires maintenance and the seafloor-surface link is fragile. In addition, these buoys are dangerous with regard to navigation.
The novel deep-sea cabled network scope of the invention stems from the following observations:
The first observation is that a deep-sea cable does not need to be particularly protected. The problems faced on the telecommunication cables in use happen mostly near the coast and at shallow depths. They are the result of anchoring activities of ships, fishing activities and fish bites. That is why in these landfall areas, the telecommunication cables are protected by external armor. Their weight is about ten tons per kilometer and their tensile resistance can reach a hundred tons. In addition, in order to perfect their protection they are usually trenched at the bottom of a trench. In deep sea (beyond 1500 metres), due to the low risk level, the cables do not need to be protected and besides, do not comprise external protection other than their plastic insulation. However, these cables remain heavy and resistant due to their deployment method from the surface (heavy to be laid at high speed and resistant to be laid at great depths).
The second observation is that low-power electronics associated with high-performance batteries enable the supply of sensors for many years. Microprocessors on standby associated with low-power clocks allow for the sampling of the measurements and the transmission of data regularly with minimum energy use. Such Hertzian transmission networks exist ashore. Weather sensor acquisition stations are a standard illustration of this type of electronics. They allow for the saving and transmission of data for many years from the energy contained in a very small battery.
The conclusion resulting from the observations established above is the following:
If the network of sensors is of a stand-alone type, the cable does not need its electric conductor anymore. If the cable is deployed close to the sea floor, it does not need to be heavy and resistant. And if the length of the network's transport segments is less than one hundred kilometers (which corresponds to the need with regard to the average distance between the points-of-use), such a micro-cable can thus be carried, deployed and connected from node to node by an underwater vehicle. Thus, the scientific users can set up, complete and maintain their own sensor networks from the scientific means they dispose of (namely, the oceanographic ships carrying underwater vehicles) without the need for costly cable ships that are in short supply. Thus, the sensors are deployed and connected during the actual set-up of the network with the same means.
A micro-cable comprising one or two optical fibres as well as an external longitudinal reinforcement has a diameter of about two millimeters and can resist a tension of about a hundred kilograms. Such a micro-cable is a hundred times lighter and ten times cheaper than a conventional telecommunications cable. The volume and weight of a transport segment is such that it can be deployed directly on the sea floor by an underwater vehicle.
The present invention is a deep-sea network having independent transport segments and made by means of optical micro-cable spools directly unwound on the sea floor by an underwater vehicle. The nodes of the network are stand-alone switches (that is, energy-autonomous type switches) whereon the ends of the transport segments and local sensors are connected on the sea floor.
The scope of the present invention is a method of producing a deep-sea network comprising main and secondary transport segments, nodes arranged on the points-of-use and local sensors characterised in that:                the transport segments are unwound independently by means of optical micro-cable spools which are provided with end connectors and borne by a deployment device implemented on the sea floor by an underwater vehicle,        the transport segment ends and the local sensors are connected at the sea floor, by an underwater vehicle, to the nodes which are stand-alone switches, so that each micro-cable is connected by its end connectors to two successive nodes of the network.        
The present invention also relates to a deep-sea network that can be obtained by the method previously described, comprising main and secondary transport segments, nodes arranged on the points-of-use and local sensors, wherein the transport segments are independent and are each formed by an optical micro-cable provided with end connectors, the nodes are stand-alone switches whereon the ends of the transport segments and the local sensors are connected on the sea floor, each micro-cable being connected by its end connectors to two successive nodes of the network.
Each transport segment is advantageously formed by a micro-cable of a diameter equal to or less than 5 mm, preferably equal to or less than 3 mm, for example about 2 mm.
The present invention also relates to a deployment device for the implementation, of the method described previously, wherein it comprises a frame, a micro-cable rotary spool fixed on this frame and of the node fixed on the rotary spool.